This application relates to a system control technique for eliminating or limiting the amount of liquid refrigerant passing through the compressor. This control technique can, for example, be applied to a suction modulation valve (“SMV”) control.
Refrigerant systems are known, and are utilized in applications such as refrigeration, air conditioning or heat pumps. Typically, a compressor compresses a refrigerant and delivers that refrigerant to a downstream condenser. Refrigerant from the condenser passes through an expansion device, and then through an evaporator. From the evaporator, the refrigerant returns to the compressor.
The refrigerant changes state as it moves through the refrigerant system, and at times it may be in a liquid state, a vapor state or a in a two-phase state where both liquid and vapor are present. If too much liquid refrigerant reaches the compressor, undesirable consequences can occur. This condition is known as “flooding.” If flooding is not controlled, it can lead to damage to internal compressor elements such as compression element components, couplings, bearings, etc. The potential damage from flooding can be a result of flooding at start-up conditions, or running the compressor flooded during continuous operation. Some degree of flooding on start up may not be avoidable, as refrigerant may leak through the expansion device during an off cycle and collect in the evaporator or compressor sump. When refrigerant builds up in the evaporator during an off cycle the SMV can act as an expansion device. Some degree of flooding can also be present during the continuous compressor operation, for example, due to inability of the expansion device to maintain a vapor phase at the compressor entrance (this can occur for example is the expansion device is oversized for a particular operating condition causing more than a desirable amount of refrigerant to pass through the expansion device). To prevent compressor damage and improve system operation it is desirable to eliminate flooding or reduce the amount of flooding.